1. Field of the Invention
The present invention relates to a liquid crystal display element using, as a liquid crystal display material, liquid crystals that molecular orientation state is cholesteric phase (i.e., cholesteric liquid crystals), and in particular to a liquid crystal display element with a superior physical durability.
2. Description of the Related Art
Recent years have witnessed the beginning of the popularization of different techniques of radio frequency identification (RFID), including noncontact type IC cards, RF tags, and other such techniques, that are durable and convenient for use in industrial fields such as logistics, transportation, and other such fields that utilize a contact type IC card, barcode, or other such device. It is predicted that in the future there will be an accelerated prevalence of cards and tags performing radio communications with external apparatuses with along with the development of new application fields such as electronic money.
While excelling in information recording, the IC card has a problem in that its record content cannot be confirmed until a dedicated apparatus reads it. It is a problem since it is desired that the record content be confirmed for reward cards and coupon cards utilized in the public transportation field. For the conventional contact type IC cards, it has been proposed that there be a display that uses a magnetic flake that functions by utilizing a visible medium by means of thermal writing using substrate 74 on which a solid common electrode 74a is featured. The light absorption layer 75 turns a transparent state of the cholesteric liquid crystal into an opaque or black display. The light absorption layer 75 may be formed either on the inside of the common substrate or on the outside thereof. Alternatively, the common electrode 74 may be formed by a material having a light absorption property (in which case a process for forming a light absorption layer is not required).
(4) Next, a segment substrate 76 and a common substrate 77, both of which are individually formed as described above, are laminated via a heating process.
(5) Next, the liquid crystals are injected from the liquid crystal injection hole of the liquid crystal layer 77 and all the segments 63 are filled with the liquid crystals by way of the liquid crystal injection paths 62 and 64. The liquid crystals can be injected by means of, for example, a vacuum injection method.
For the LCE element 70 shown in FIG. 9, the common electrode 74a of the common substrate 77 is electrically connected to a transfer electrode 71a of the segment substrate 76 with a conductive adhesive or other such device in order to draw the common electrode 74a of the common substrate 77 out of the segment substrate 76. The wall structure 73 comprises an adhesive property; a sealing material of a common liquid crystal structure may, however, be equipped on the periphery of the LCD element.
In a cholesteric LCD element that does not use a diffraction plate, the liquid crystals remain in the liquid crystal injection path, and therefore a light shield mask is required to hide the liquid crystals remaining in the liquid crystal injection path (refer to the above described process (1)).
In the case of the LCD apparatus of the antiferroelectric liquid crystal shown in FIG. 4, only a few parts of the segments (i.e., segments at the upper, middle and lower parts of the right a leuco dye. Such a contact type IC card requires a dedicated use apparatus for inserting the IC card, with the dedicated use apparatus being built in with a display/write apparatus equipped with a magnetic head or thermal head. However, a write head comprised by a contact type IC card dedicated use apparatus cannot be equipped for use in noncontact type IC cards and RF tags, which are predicted to become more popular in the future. Consequently, a display must be realized that employs an electric signal that is supplied wirelessly; thus, a display that functions by means of a liquid crystal display (LCD) system and that is electrically drivable is required, such as an electrophoresis system or other such system.
Patent documents 1 and 2 below, for which applications have been submitted to the Japan Patent Office, are available as reference documents related to an IC card and an RF tag, either of which can comprise a display device.
Patent document 1: Japanese registered utility model Kokai number (1995)30384
Patent document 2: Japanese unscreened Patent Application Kokai number (2002)236891
Patent document 1 (on page 3, column 6, line 37) also notes the consideration of a noncontact type IC card and of an RF tag. Patent document 2 describes the structure of a noncontact type IC card in detail. Patent documents 1 and 2 propose an LCD element as one candidate for display elements. If an LCD element is used as a display element for a noncontact type IC card, ferroelectric liquid crystal (FLC) and cholesteric liquid crystal (ChLCD), both of which continue to show their displays after the power is turned off, are conceivable candidates for the liquid crystal material. The cholesteric liquid crystal is sometimes called a chiral nematic liquid crystal.
The reason that conventional LCD elements are unable to act as display elements for an IC card or an RF tag is their lack of physical durability. A display element cannot be adopted for an IC card unless, for example, it possesses bending resistance and it is environmental test, both of which characteristics are specified by Japanese Industry Standard (JIS), and common LCD elements have not been able to meet those conditions.
For example, if an IC card body is 85 mm on the long side, it must be able to withstand being bent 2 cm greater or equal 500 times at the center thereof without breaking. Conventional LCD elements have not been able to pass this durability test due to substrate breakage, the orientation of the liquid crystal molecules being disturbed, the seal material peeling off, and other such problems.
The contact type and hybrid type (having functions of both contact and noncontact types) IC cards undergo a strong pressure from a transport roller (i.e., a roller pressure) on the card surface when they are inserted into a readout apparatus. The conventional LCD element suffers from the liquid crystals being pushed to one side by the roller pressure, resulting in a broken seal, spillage of the liquid crystal, and eventually loss of its function as an LCD element.
The applicant of the present invention (noted as “present applicant” or “we” hereinafter) has accordingly proposed, by virtue of patent document 3 (i.e., Japanese Patent Application Kokai number (2003)998646), a thin structure LCD element using a cholesteric liquid crystal which is mountable onto an IC card of a standard thickness (of 0.76 mm) while meeting the above described requirement of the JIS specification. In the meantime, patent document 4 (i.e., Japanese unscreened Patent Application Kokai number 2002(328374)) has proposed a structure of an LCD element that improves durability by using an antiferroelectric liquid crystal (AFLC). However, in an AFLC, it is fundamentally difficult to maintain the orientation of the liquid crystals and it has a weakness in anti-shock resistance, and hence is inapplicable to an IC card. It also requires the use of a polarization plate, making it difficult to mount it onto an IC card of a standard thickness (of 0.76 mm).
The LCD element proposed by the above noted patent document 3 meets the durability requirement as per the JIS specifications. A further problem, however, remains to be solved: a cholesteric liquid crystal is faced with the situation of a human finger (noted as “finger” hereinafter) pressing, or fingers pinching, the display surface of the LCD element and thus warping or twisting it, resulting in such a force being added to the cholesteric liquid crystal changing display states. Additionally, the cholesteric liquid crystal has returns to its original state by being driven to display again.
Considering application to the IC card, the fact of its display being changed by a mere pressing with a finger (i.e., a pressing pressure) is a large problem, hampering the convenience of use even if a display state is restored by being to driven to display. The present applicant has carried out a verification test on the LCD element disclosed by patent document 3, obtaining a result verifying the fact that the configuration of the LCD element allows the display to change under the pressure of a finger pressing upon it (i.e., finger pressure).
FIG. 1 is a diagram showing the overall structure of the LCD element proposed by patent document 3, and FIG. 2 is an exploded diagram of the LCD element. FIG. 3 is a horizontal cross-sectional diagram of a wall structure (i.e., a wall material) and of a display part equipped on the inside of the LCD element. FIG. 4 is a diagram showing a part of a cross-section in the direction parallel to a layer including the liquid crystal cell and partition wall of the LCD element disclosed by patent document 4.
The LCD element proposed by patent document 3 is configured to sandwich a wall structure 3, a display part 4 and a light shield mask 5 between a segment board 1 and a common board 2.
As shown in FIG. 2, the wall structure 3 and display part 4 are equipped between the common board 2 and light shield mask 5. The thickness of the layer including the wall structure 3 and display part 4 is a few micrometers. In the example shown in FIG. 2, the display part 4 is constituted by four segment blocks 4a. The following description calls the layer including the wall structure 3 and display part 4 a liquid crystal cell layer 10 for convenience.
In close observation it can be seen that the liquid crystal cell layer 10 comprises a liquid crystal injection path 11 and a buffer part 12, in addition to the wall structure 3 and display part 4. The liquid crystal injection path 11 is a passage equipped for injecting liquid crystals into the display part 4 (i.e., the liquid crystal cell), and therefore the path 11 is on the left side of the first stage segment block 4a and between the adjacent segment blocks 4a. The liquid crystal injection path 11 is configured to be straight. The liquid crystals for the liquid crystal cell layer 10 are injected from the left end part 11a of the liquid crystal injection path 11 connecting to the left end of the first stage segment block 4a. The injected liquid crystals are injected into the last stage segment block 4a after being led through the liquid crystal injection path 11 and segment blocks 4a. The buffer part 12 connected to the right end of the last stage segment block 4a is equipped for encapsulating an extraneous volume of air flowing in when vacuum-injecting the liquid crystals. As a result, the liquid crystals are also filled in the buffer part 12 in terms of this structure.
The upper part of the wall structure 3 is equipped with the light shield mask (i.e., a light shield film) 5 which is a mask, being formed on the segment board 1, for preventing liquid crystal injection zones (i.e., the liquid crystal injection path 11 and buffer part 12), which are not required for a segment display in the liquid crystal cell layer 10, from functioning as display zones. The light shield mask 5 comprises light transmission parts 5a of a form corresponding to the segment pattern of the display part 4. The width of the light transmission part 5a is configured to be smaller than that of the segment block 4a of the display part 4, considering positioning margin and visibility. The light shielding function of the light shield mask 5 enables the display part 4 to display a segment with good visibility and contrast.
FIG. 4 is a horizontal cross-sectional diagram of a liquid crystal layer of the liquid crystal display apparatus proposed by patent document 4. Referring to FIG. 4, the whitened parts are the display parts (i.e., segments) 20 corresponding to the parts equipped with liquid crystal cells, or liquid crystal injection paths 28. Patent document 4 expresses each segment as a display part (or a liquid crystal cell). The liquid crystal injection paths 28 are indicated by six parallel thin lines, while the display parts 20 are indicated by rectangles or approximate rectangles that are thicker than the thin lines. The left end of the liquid crystal injection paths 28 is configured as a liquid crystal injection part 29. The display parts 20 are injected with an antiferroelectric liquid crystal by way of the liquid crystal injection part 29 and liquid crystal injection paths 28. The blackened parts are partition walls 27.
As described above, the LCD elements according to patent documents 3 and 4 are configured to be similar to each other; the main difference between the two is the use of different liquid crystal materials. The LCD element according to patent document 3 uses a cholesteric liquid crystal while the LCD apparatus according to patent document 4 uses an antiferroelectric liquid crystal.
Both the LCD element according to patent document 3 and the LCD apparatus according to patent document 4 are faced with the problem of display states being changed by finger pressure being applied onto the display surface or warping of the element (or the apparatus).